Pressure sensitive adhesives (PSA) are well known and are used in many industrial, consumer and medical applications. Pressure sensitive adhesives are formulations typically comprising an elastomeric polymer, a tackifier, and optionally an oil or other additives. These adhesives remain permanently tacky and adhere instantaneously to a wide variety of surfaces with the application of a small amount of pressure. Pressure sensitive adhesives are generally used in the form of adhesive assemblies comprising a coating on a backing, such as in adhesive bandages, wound dressings, transdermal delivery devices, tapes, stencils, wall paper, envelopes, stamps, and floor tiles.
For many applications, it is desirable to be able to remove the adhesive assembly from the surface without significant force, so that the surface or substrate, for example, newly healed skin, is not damaged. For this reason, switchable adhesives, which undergo a reduction in peel strength with a change in conditions, have been developed. Switchable adhesives that exhibit a reduction in peel strength upon contact with water or exposure to UV radiation are known. Particularly useful for some adhesive applications are temperature switchable adhesives, which undergo a reduction in peel strength with a temperature change (see for example, Stewart, U.S. Pat. Nos. 5,156,911 and 5,387,450; Schmitt et al., U.S. Pat. No. 5,412,035; and Burch, U.S. Pat. No. 7,399,800).
Typically, these temperature switchable pressure sensitive adhesives have high peel strength and low tack below the switching temperature and low peel strength but high tack above the switching temperature. Some temperature switchable pressure sensitive adhesives, such as those described by Stewart et al. (U.S. Pat. Nos. 5,387,450 and 5,387,450), have low peel strength and low tack below their switching temperature and high peel strength and high tack above the switching temperature. Therefore, the temperature switchable adhesive assemblies must be either warmed or cooled in order to activate adhesion to a substrate.
In view of the above, the need exists for new temperature switchable adhesive assemblies which maintain tack above and below the switching temperature.